Dielectric Properties of Polymer/Ferroelectric Ceramic Composites from 100 Hz to 10 GHz

Highly Selective Ionic Gel-Based Gas Sensor for Halogenated Volatile Organic Compound Detection: Effect of Dipole-Dipole Interaction

Halogenated volatile organic compounds (abbreviated as X-VOCs) are a class of hazardous gas pollutants that are difficult to detect due to their thermal stability, chemical inertness, and poisoning effect on gas sensors at high temperatures. In this work, room-temperature detection of X-VOCs is achieved using a surface acoustic wave (SAW) gas sensor coated with a 1-ethyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide (EMIM-TFSI)-based ionic gel film. We experimentally verify that the high selectivity of the ionic gel-based SAW gas sensor for X-VOCs is due to the presence of halogen atoms in these gas molecules. Meanwhile, the sensor has very little response to common organic gases such as ethanol, isopropanol, and acetone, reflecting a low cross-sensitivity to nonhalogenated VOCs. This unique advantage shows potential applications in selective detection of X-VOCs and is validated by comparison with a commercial metal oxide semiconductor (MOS) sensor. Furthermore, the internal sensing mechanism is explored by the density functional theory (DFT) method. The simulation results demonstrate that the X-VOC molecules are highly polarized by the inductive effect of halogen atom substitution, which is beneficial for being adsorbed by the EMIM-TFSI ionic liquid via dipole-dipole interaction.

Dielectric characterization of paraelectric particle-loaded polymer matrix composites and commercial photoresins at W-band frequencies

This work presents W-band (75-110 GHz) dielectric characterization of commercially available photoresins in their neat state, as well as in polymer matrix composite (PMC) mixtures with various loading concentrations of the paraelectric barium strontium titanate (BST). Due to difficulties 3D printing the BST-loaded PMC resins detailed within, a custom curing and casting process was used to fabricate testable PMC samples, which were synthesized to demonstrate the dielectric functionalization of the underlying polymer matrix. Dielectric characterization of the PMCs confirmed the functionalization of our composites when compared to the commercial photoresins. For example, a volumetric loading concentration of 25 vol % BST increased the dielectric permittivity (ε_r ) from 2.78 to 9.60 and the loss tangent (tanδ) from 0.022 to 0.114. These results indicate that the realization of UV-cured photoresins with "designer-dielectric" functionalization based on vol % of filler are strong candidates for use in stereolithography (SLA) 3D printing applications. To accomplish this, and with a special interest for radio/microwave/terahertz (RF/MW/THz) applications, we highlight the need for both (a) better photoresin matrix materials with lower intrinsic tanδ and (b) selection criteria related to the size/geometry and electronic properties of potential filler materials to maintain the printability of PMC photoresins in SLA systems.

Dielectric Behavior of Thin Polymerized Composite Layers Fabricated by Inkjet-Printing

A detailed study of the dielectric behavior of printed capacitors is given, in which the dielectric consists of a thin (<1 µm) ceramic/polymer composite layer with high permittivities of ε_r 20-69. The used ink contains surface-modified Ba_0.6Sr_0.4TiO₃ (BST), a polymeric crosslinking agent and a thermal initiator, which allows the immediate polymerization of the ink during printing, leading to homogenous layers. To validate the results of the calculated permittivities, different layer thicknesses of the dielectric are printed and the capacitances, as well as the loss factors, are measured. Afterwards, the exact layer thicknesses are determined with cross sectional SEM images of ion-etched samples. Then, the permittivities are calculated with the known effective area of the capacitors. Furthermore, the ink composition is varied to obtain different ceramic/polymer ratios and thus different permittivities. The packing density of all composites is analyzed via SEM to show possible pores and validate the target ratio, respectively. The correlation between the chosen ratio and the measured permittivity is discussed using models from the literature. In addition, the leakage current of some capacitors is measured and discussed. For that, the dielectric was printed on different bottom electrodes as the nature of the electrode was found to be crucial for the performance.

Parallel Structure Enhanced Polysilylaryl-enyne/Ca0.9La0.067TiO3 Composites with Ultra-High Dielectric Constant and Thermal Conductivity

With the rapid development of the microwave communication industry, microwave dielectric materials have been widely studied as the medium of signal transmission. Nowadays, with the increase in communication frequency, devices are miniaturized, and dielectric materials are required to have higher dielectric constants. At the same time, the miniaturization of devices brings about an increase in power density, which puts forward higher requirements for the thermal conductivity of materials. In this work, polysilylaryl-enyne (PSAE) and Ca_0.9La_0.067TiO₃ (CLT) were chosen as the matrix and filler, respectively, to construct a parallel model composite through a freeze casting method and a 0-3 model composite through the direct mixing method, respectively. After comparing the microstructures of the two models, their dielectric properties and thermal conductivity were measured and simulated. The parallel model composites in the stable range possess uniform parallel structures, and the solid content limit for them could be as high as 73.2%, which is much higher than that of the 0-3 model composites. While the 0-3 model composite possesses an optimal dielectric constant of 25.4 (@10 GHz) and a thermal conductivity of 0.965 W·m^-1·K^-1, the parallel model composite possesses a 2 times higher dielectric constant of 76.2 (@10 GHz) and a 1 times higher thermal conductivity of 2.095 W·m^-1·K^-1. Since the parallel model composite possesses much higher dielectric constant and thermal conductivity than traditional 0-3 model composites, it can be an excellent candidate for microwave communication.

Piezoelectric Ceramic/Photopolymer Composites Curable with UV Light: Viscosity, Curing Depth, and Dielectric Properties

Four piezoelectric ceramic materials with varying particle sizes and geometries are added up to 30 vol.% to a photopolymer resin to form UV-curable piezoelectric composites. Such composites solidify in a few minutes, can be used in UV-curing-based 3D printing processes, and can achieve improved sensor performance. The particle dispersion with ultrasonication shows the most homogeneous particle dispersion with ethanol, while two other solvents produced similar results. The viscosities of the prepared suspensions show some dependency on the particle size. The curing depth results show a strong dependency on the ceramic particle size, the difference in refractive index, and the particle size distribution, whereby composites filled with PZT produced the worst results and composites filled with KNN produced the highest curing depths. The SEM images show a homogeneous dispersion of ceramic particles. The highest dielectric properties are also shown by KNN-filled composites, while BTO and PZT produced mixed results of dielectric constants and dielectric losses. KNN-filled composites seem to be very promising for further 3D-printable, lead-free piezoelectric composite development.

Electromagnetic field controlled domain wall displacement for induced strain tailoring in BaTiO3-epoxy nanocomposite

Failure in an epoxy polymer composite material is prone to initiate by the coalescence of microcracks in its polymer matrix. As such, matrix toughening via addition of a second phase as rigid or/and rubber nano/micro-particles is one of the most popular approaches to improve the fracture toughness across multiple scales in a polymer composite, which dissipates fracture energy via deformation mechanisms and microcracks arrest. Few studies have focused on tailorable and variable toughening, so-called ‘active toughening’, mainly suggesting thermally induced strains which offer slow and irreversible toughening due to polymer’s poor thermal conductivity. The research presented in the current article has developed an instantaneous, reversible extrinsic strain field via remote electromagnetic radiation. Quantification of the extrinsic strain evolving in the composite with the microwave energy has been conducted using in-situ real-time fibre optic sensing. A theoretical constitutive equation correlating the exposure energy to micro-strains has been developed, with its solution validating the experimental data and describing their underlying physics. The research has utilised functionalised dielectric ferroelectric nanomaterials, barium titanate (BaTiO₃), as a second phase dispersed in an epoxy matrix, able to introduce microscopic electro-strains to their surrounding rigid epoxy subjected to an external electric field (microwaves, herein), as result of their domain walls dipole displacements. Epoxy Araldite LY1564, a diglycidyl ether of bisphenol A associated with the curing agent Aradur 3487 were embedded with the BaTiO₃ nanoparticles. The silane coupling agent for the nanoparticles’ surface functionalisation was 3-glycidoxypropyl trimethoxysilane (3-GPS). Hydrogen peroxide (H₂O₂, 30%) and acetic acid (C₂H₄O₂, 99.9%) used as functionalisation aids, and the ethanol (C₂H₆O, 99.9%) used for BaTiO₃ dispersion. Firstly, the crystal microstructure of the functionalised nanoparticles and the thermal and dielectric properties of the achieved epoxy composite materials have been characterised. It has been observed that the addition of the dielectric nanoparticles has a slight impact on the curing extent of the epoxy. Secondly, the surface-bonded fibre Bragg grating (FBG) sensors have been employed to investigate the real-time variation of strain and temperature in the epoxy composites exposed to microwaves at 2.45 GHz and at different exposure energy. The strains developed due to the in-situ exposure at composite, adhesive and their holding fixture material were evaluated using the FBG. The domain wall induced extrinsic strains were distinguished from the thermally induced strains, and found that the increasing exposure energy has an instantaneously increasing effect on the development of such strains. Post-exposure Raman spectra showed no residual field in the composite indicating no remnant strain field examined under microwave powers < 1000 W, thus suggesting a reversible strain introduction mechanism, i.e. the composite retaining its nominal properties post exposure. The dielectric composite development and quantifications presented in this article proposes a novel active toughening technology for high-performance composite applications in numerous sectors.

Raising Dielectric Permittivity Mitigates Dopant-Induced Disorder in Conjugated Polymers

Conjugated polymers need to be doped to increase charge carrier density and reach the electrical conductivity necessary for electronic and energy applications. While doping increases carrier density, Coulomb interactions between the dopant molecules and the localized carriers are poorly screened, causing broadening and a heavy tail in the electronic density-of-states (DOS). The authors examine the effects of dopant-induced disorder on two complimentary charge transport properties of semiconducting polymers, the Seebeck coefficient and electrical conductivity, and demonstrate a way to mitigate them. Their simulations, based on a modified Gaussian disorder model with Miller-Abrahams hopping rates, show that dopant-induced broadening of the DOS negatively impacts the Seebeck coefficient versus electrical conductivity trade-off curve. Increasing the dielectric permittivity of the polymer mitigates dopant-carrier Coulomb interactions and improves charge transport, evidenced by simultaneous increases in conductivity and the Seebeck coefficient. They verified this increase experimentally in iodine-doped P3HT and P3HT blended with barium titanate (BaTiO3 ) nanoparticles. The addition of 2% w/w BaTiO3 nanoparticles increased conductivity and Seebeck across a broad range of doping, resulting in a fourfold increase in power factor. Thus, these results show a promising path forward to reduce the dopant-charge carrier Coulomb interactions and mitigate their adverse impact on charge transport.

Mechanical Behaviour of Large Strain Capacitive Sensor with Barium Titanate Ecoflex Composite Used to Detect Human Motion

In this paper, the effect of strain rate on the output signal of highly stretchable interdigitated capacitive (IDC) strain sensors is studied. IDC sensors fabricated with pristine Ecoflex and a composite based on 40 wt% of 200 nm barium titanate (BTO) dispersed in a silicone elastomer (Ecoflex 00-30TM) were subjected to 1000 stretch and relax cycles to study the effect of dynamic loading conditions on the output signal of the IDC sensor. It was observed that the strain rate has no effect on the output signal of IDC sensor. To study the non-linear elastic behaviour of pristine Ecoflex and composites based on 10, 20, 30, 40 wt% of 200 nm BTO filler dispersed in a silicone elastomer, we conducted uniaxial tensile testing to failure at strain rates of ~5, ~50, and ~500 mm/min. An Ogden second-order model was used to fit the uniaxial tensile test data to understand the non-linearity in the stress-strain responses of BTO-Ecoflex composite at different strain rates. The decrease in Ogden parameters (α1 and α2) indicates the decrease in non-linearity of the stress-strain response of the composite with an increase in filler loading. Scanning electronic microscopy analysis was performed on the cryo-fractured pristine Ecoflex and 10, 20, 30, and 40 wt% of BTO-Ecoflex composites, where it was found that 200 nm BTO is more uniformly distributed in Ecoflex at a higher filler loading levels (40 wt% 200 nm BTO). Therefore, an IDC sensor was fabricated based on a 40 wt% 200 nm BTO-Ecoflex composite and mounted on an elastic elbow sleeve with supporting electronics, and successfully functioned as a reliable and robust flexible sensor, demonstrating an application to measure the bending angle of an elbow at slow and fast movement of the arm. A linear relationship with respect to the elbow bending angle was observed between the IDC sensor output signal under a 50% strain and the deflection of the elbow of hand indicating its potential as a stretchable, flexible, and wearable sensor.

Application of Perovskite Layer to Rotor for Enhanced Stator-Rotor Capacitance for PMSM Shaft Voltage Reduction

Adjustable speed drives use Pulse Width Modulation (PWM) to switch DC-bus voltage for the synthesis of three-phase voltages to provide power to the permanent magnet synchronous motor (PMSM). This switching action produces very short rise and fall times and Common Mode Voltage (CMV) in the motor winding, exciting the parasitic capacitances inherent to the motor geometry. These parasitic capacitances give rise to shaft voltage due to a voltage divider action. Therefore, in this paper, first, motor parasitic capacitances and voltage divider action is explained. Second, the Barium Titanate (BTO) layer is coated onto the rotor to enhance stator-to-rotor compound capacitance and a simulation is performed showing the dependence of the shaft voltage on the permittivity of the perovskite (BTO) layer. The rotor BTO layer reduces the bearing voltage ratio as well. Third, experimental results are presented showing effectiveness of the application of the BTO layer to rotor and reduction of shaft voltage of the motor in anticipation to mitigate the damaging electric discharge machining (EDM) bearing currents. Likewise, the experiment shows that the magnetic design of the motor is not affected by the BTO layer to rotor.

The electrical and mechanical properties of Cadmium chloride reinforced PVA:PVP blend films

In this study, pure polymer blend (PVA:PVP) film and salt (CdCl2·H2O) reinforced polymer blend films were prepared at different weight ratios (10 wt%, 20 wt%, 40 wt%) using the casting method. The effect of the salt weight ratio on the dielectric properties of the polymer blend films reinforced by CdCl2·H2O salt were investigated, and the experimental results showed that the dielectric constant and the dielectric loss factor decreased as the frequency increased for all polymer blend films. Moreover, the above-mentioned properties increased with increasing salt weight ratios at the same frequency. The experimental results also showed an increase in AC electrical conductivity with increasing frequency, for all polymer blend films, and the AC electrical conductivity also increased with an increase in the weight ratio of the salt at the same frequency. The effect of the salt weight ratio on the mechanical properties of the salt-reinforced PVA:PVP polymer blend films was also studied. The experimental results obtained from the tensile test of the salt-reinforced polymer blend films show significant change in the values of tensile strength, elongation at break, and Young’s modulus with increasing salt weight ratios; the hardness value first increases then decreases with increasing salt weight ratios, and the fracture energy value increases with increasing salt weight ratios, thus they could be good candidates for hard adhesives with low flexibility.

High-k Polymer Nanocomposite Materials for Technological Applications

Understanding the properties of small molecules or monomers is decidedly important. The efforts of synthetic chemists and material engineers must be appreciated because of their knowledge of how utilize the properties of synthetic fragments in constructing long-chain macromolecules. Scientists active in this area of macromolecular science have shared their knowledge of catalysts, monomers and a variety of designed nanoparticles in synthetic techniques that create all sorts of nanocomposite polymer stuffs. Such materials are now an integral part of the contemporary world. Polymer nanocomposites with high dielectric constant (high-k) properties are widely applicable in the technological sectors including gate dielectrics, actuators, infrared detectors, tunable capacitors, electro optic devices, organic field-effect transistors (OFETs), and sensors. In this short colloquy, we provided an overview of a few remarkable high-k polymer nanocomposites of material science interest from recent decades.

High dielectric thin films based on barium titanate and cellulose nanofibrils

A series of composite films based on tetragonal barium titanate (BTO) and cellulose nanofibrils (CNF) with high dielectric constant are prepared using a casting method in aqueous solution. No organic solvent is involved during the preparation, which demonstrates the environmental friendliness of the novel material. With less than 30 wt% of filler loading, the excellent distribution of BTO nanoparticles within the CNF matrix is revealed by the FE-SEM images. The dielectric constant of the CNF/BTO (30 wt%) composite film reaches up to 188.03, which is about seven times higher than that of pure CNF (25.24), while the loss tangent only rises slightly from 0.70 to 1.21 (at 1 kHz). The thin films kept their dielectric properties on an acceptable level after repeatedly twisting or rolling 10 times. The improvement of thermal stability is observed with the presence of BTO. The outstanding dielectric properties of the CNF/BTO composite film indicates its great potential to be utilized in energy storage applications.

The high dielectric thin films based on cellulose fibrils and tetragonal barium titanate exhibit excellent dielectric properties, flexibility and durability.

Dielectric properties of solution-processed BaTiO3–styrene butadiene styrene nanocomposite films

Polymer–ceramic nanocomposite films comprising ceramic nanoparticles dispersed in a polymer matrix (0–3 composites) have garnered increasing interest due to their superior performance characteristics, and can be used in flexible modern electronics and energy storage systems.

Fabrication and Characterization of Fully Inkjet Printed Capacitors Based on Ceramic/Polymer Composite Dielectrics on Flexible Substrates

The preparation of fully inkjet printed capacitors containing ceramic/polymer composites as the dielectric material is presented. Therefore, ceramic/polymer composite inks were developed, which allow a fast one-step fabrication of the composite thick films. Ba_0.6Sr_0.4TiO₃ (BST) is used as the ceramic component and poly(methyl methacrylate) (PMMA) as the polymer. The use of such composites allows printing on flexible substrates. Furthermore, it results in improved values for the permittivity compared to pure polymers. Three composite inks with varying ratio of BST to PMMA were used for the fabrication of composite thick films consisting of 33, 50 and 66 vol% BST, respectively. All inks lead to homogeneous structures with precise transitions between the different layers in the capacitors. Besides the microstructures of the printed thick films, the dielectric properties were characterized by impedance spectroscopy over a frequency range of 100 Hz to 200 kHz. In addition, the influence of a larger ceramic particle size was investigated, to raise permittivity. The printed capacitors exhibited dielectric constants of 20 up to 55 at 1 kHz. Finally, the experimental results were compared to different theoretical models and their suitability for the prediction of ε_composite was assessed.

Barium titanate at the nanoscale: controlled synthesis and dielectric and ferroelectric properties

The current trend in the miniaturization of electronic devices has driven the investigation into many nanostructured materials. The ferroelectric material barium titanate (BaTiO3) has garnered considerable attention over the past decade owing to its excellent dielectric and ferroelectric properties. This has led to significant progress in synthetic techniques that yield high quality BaTiO3 nanocrystals (NCs) with well-defined morphologies (e.g., nanoparticles, nanorods, nanocubes and nanowires) and controlled crystal phases (e.g., cubic, tetragonal and multi-phase). The ability to produce nanoscale BaTiO3 with controlled properties enables theoretical and experimental studies on the intriguing yet complex dielectric properties of individual BaTiO3 NCs as well as BaTiO3/polymer nanocomposites. Compared with polymer-free individual BaTiO3 NCs, BaTiO3/polymer nanocomposites possess several advantages. The polymeric component enables simple solution processibility, high breakdown strength and light weight for device scalability. The BaTiO3 component enables a high dielectric constant. In this review, we highlight recent advances in the synthesis of high-quality BaTiO3 NCs via a variety of chemical approaches including organometallic, solvothermal/hydrothermal, templating, molten salt, and sol-gel methods. We also summarize the dielectric and ferroelectric properties of individual BaTiO3 NCs and devices based on BaTiO3 NCs via theoretical modeling and experimental piezoresponse force microscopy (PFM) studies. In addition, viable synthetic strategies for novel BaTiO3/polymer nanocomposites and their structure-composition-performance relationship are discussed. Lastly, a perspective on the future direction of nanostructured BaTiO3-based materials is presented.

Carbon-based polymer nanocomposites as dielectric energy storage materials

Nanostructured polymeric materials based on conductive nanofillers have promising applications in the energy storage field owing to the extraordinary characteristics of the nanofillers. Conductive nanofillers, such as graphene nanoplatelets, are characterized by small size, extraordinary surface area to volume ratio, high aspect-ratio and extremely low electrical resistivity. In this work, the dielectric behaviors and the corresponding energy storage capabilities of high aspect-ratio carbon nanofiller/polymer composites were reviewed. At the electrical percolation point, a conductive composite exhibits a sudden and remarkable enhancement in dielectric constant and dielectric loss. The challenge is to maintain the increase in dielectric constant while preventing the increase in dielectric loss. Various physical and chemical methodologies have been followed to overcome this challenge including surface chemistry modifications, physical alignment of nanofillers and utilizing of hybrid mixtures. Promising results were reported to minimize the energy loss due to the conductive network formation. Nanocomposites with a dielectric constant of 10³ and dielectric loss of only 0.08 were successfully fabricated. However, more work is still needed for a further enhancement in dielectric constant and reduction in the energy loss and to improve the storage capabilities of the nanocomposites.

Highly Stretchable Capacitive Sensor with Printed Carbon Black Electrodes on Barium Titanate Elastomer Composite

Wearable electronics and soft robotics are emerging fields utilizing soft and stretchable sensors for a variety of wearable applications. In this paper, the fabrication of a highly stretchable capacitive sensor with a printed carbon black/Ecoflex interdigital capacitor is presented. The highly stretchable capacitive sensor was fabricated on a substrate made from barium titanate⁻EcoflexTM 00-30 composite, and could withstand stretching up to 100%. The designed highly stretchable capacitive sensor was robust, and showed good repeatability and consistency when stretched and relaxed for over 1000 cycles.

Synergistic Enhancement of Thermal Conductivity and Dielectric Properties in Al₂O₃/BaTiO₃/PP Composites

Multifunctional polymer composites with both high dielectric constants and high thermal conductivity are urgently needed by high-temperature electronic devices and modern microelectromechanical systems. However, high heat-conduction capability or dielectric properties of polymer composites all depend on high-content loading of different functional thermal-conductive or high-dielectric ceramic fillers (every filler volume fraction ≥ 50%, i.e., ffiller ≥ 50%), and an overload of various fillers (fthermal-conductivefiller + fhigh-dielectricfiller > 50%) will decrease the processability and mechanical properties of the composite. Herein, series of alumina/barium titanate/polypropylene (Al₂O₃/BT/PP) composites with high dielectric- and high thermal-conductivity properties are prepared with no more than 50% volume fraction of total ceramic fillers loading, i.e., ffillers ≤ 50%. Results showed the thermal conductivity of the Al₂O₃/BT/PP composite is up to 0.90 W/m·K with only 10% thermal-conductive Al₂O₃ filler, which is 4.5 times higher than the corresponding Al₂O₃/PP composites. Moreover, higher dielectric strength (Eb) is also found at the same loading, which is 1.6 times higher than PP, and the Al₂O₃/BT/PP composite also exhibited high dielectric constant ( ε r = 18 at 1000 Hz) and low dielectric loss (tan δ ≤ 0.030). These excellent performances originate from the synergistic mechanism between BaTiO₃ macroparticles and Al₂O₃ nanoparticles.

Monomer Derived Poly(Furfuryl)/BaTiO3 0-3 Nanocomposite Capacitors: Maximization of the Effective Permittivity Through Control at the Interface

Frequency stable, high permittivity nanocomposite capacitors produced under mild processing conditions offer an attractive replacement to MLCCs derived from conventional ceramic firing. Here, 0-3 nanocomposites were prepared using gel-collection derived barium titanate nanocrystals, suspended in a poly(furfuryl alcohol) matrix, resulting in a stable, high effective permittivity, low loss dielectric. The nanocrystals are produced at 60 °C, emerging as fully crystallized cubic BTO, 8 nm, paraelectric with a highly functional surface that enables both suspension and chemical reaction in organic solvents. The nanocrystals were suspended in furfuryl alcohol inside a uniquely prepared mold, in which volume fraction of nanocrystal filler (ν_f) could be varied. Polymerization of the matrix in situ at 70-90 °C resulted in a nanocomposite with a higher than anticipated effective permittivity (up to 50, with ν_f only 0.41, 0.5-2000 kHz), exceptional stability as a function of frequency, and very favorable dissipation factors (tan δ < 0.01, ν_f < 0.41; tan δ < 0.05, ν_f < 0.5). The increased permittivity is attributed to the covalent attachment of the poly(furfuryl alcohol) matrix to the surface of the nanocrystals, homogenizing the particle-matrix interface, limiting undercoordinated surface sites and reducing void space. XPS and FTIR confirmed strong interfacial interaction between matrix and nanocrystal surface. Effective medium approximations were used to compare this with similar nanocomposite systems. It was found that the high effective permittivity could not be attributed to the combination of two components alone, rather the creation of a hybrid nanocomposite possessing its own dielectric behavior. A nondispersive medium was selected to focus on the frequency dependent permittivity of the 8 nm barium titanate nanocrystals. Experimental corroboration with known theory is evident until a specific volume fraction (ν_f ≈ 0.3) where, due to a sharp increase in the effective permittivity, approximations fail to adequately describe the nanocomposite medium.

Soft Multifunctional Composites and Emulsions with Liquid Metals

Binary mixtures of liquid metal (LM) or low-melting-point alloy (LMPA) in an elastomeric or fluidic carrier medium can exhibit unique combinations of electrical, thermal, and mechanical properties. This emerging class of soft multifunctional composites have potential applications in wearable computing, bio-inspired robotics, and shape-programmable architectures. The dispersion phase can range from dilute droplets to connected networks that support electrical conductivity. In contrast to deterministically patterned LM microfluidics, LMPA- and LM-embedded elastomer (LMEE) composites are statistically homogenous and exhibit effective bulk properties. Eutectic Ga-In (EGaIn) and Ga-In-Sn (Galinstan) alloys are typically used due to their high conductivity, low viscosity, negligible nontoxicity, and ability to wet to nonmetallic materials. Because they are liquid-phase, these alloys can alter the electrical and thermal properties of the composite while preserving the mechanics of the surrounding medium. For composites with LMPA inclusions (e.g., Field's metal, Pb-based solder), mechanical rigidity can be actively tuned with external heating or electrical activation. This progress report, reviews recent experimental and theoretical studies of this emerging class of soft material architectures and identifies current technical challenges and opportunities for further advancement.

Enhanced polarization and dielectricity in BaTiO3:NiO nanocomposite films modulated by the microstructure

Parallel and vertical interfaces in vertically and parallelly aligned nanocomposite thin films have been shown to be an effective method to manipulate functionalities.

Dielectric and current–voltage characteristics of flexible Ag/BaTiO3 nanocomposite films processed at near room temperature

A room temperature processing of printed Ag/BaTiO₃ nanocomposites results in a flexible capacitor with a dielectric constant of 300.

The effect of DBP of carbon black on the dynamic self-assembly in a polymer melt

Three types of carbon black with different dibutyl phthalate (DBP) absorption have been used to study the electrical percolation behavior in thermoplastic polyurethane.

Ultra-capacitor flexible films with tailored dielectric constants using electric field assisted assembly of nanoparticles

In this study, the chaining and preferential alignment of barium titanate nanoparticles (100 nm) through the thickness direction of a polymer matrix in the presence of an electric field is shown. Application of an AC electric field in a well-dispersed solution leads to the formation of chains of nanoparticles in discrete rows oriented with their primary axis in the E-field direction due to dielectrophoresis. The change in the orientation of these chains was quantified through statistical analysis of SEM images and was found to be dependent on E-field, frequency and viscosity. When a DC field is applied a distinct layer consisting of dense particles was observed with micro-computed tomography. These studies show that the increase in DC voltage leads to increase in the thickness of the particle rich layer along with the packing density also increasing. Increasing the mutual interactions between particles due to the formation of particle chains in the "Z"-direction decreases the critical percolation concentration above which substantial enhancement of properties occurs. This manufacturing method therefore shows promise to lower the cost of the products for a range of applications including capacitors by either enhancing the dielectric properties for a given concentration or reduces the concentration of nanoparticles needed for a given property.

Studies on graphene oxide–reinforced polybenzoxazine nanocomposites

In the present work, different weight percentages (1, 3, and 5 wt%) of benzoxazine-functionalized graphene oxide (FGO) were reinforced with polybenzoxazine (PBZ) matrix by means of ring-opening polymerization. The resulting nanocomposites were characterized for their thermal, mechanical, dielectric, and optical properties using different analytical techniques. From the results of these studies, it was observed that the 5 wt% FGO-reinforced PBZ composite shows an improved glass transition temperature, thermal stability, and dielectric constant to the extent of 18%, 39%, and 197%, respectively, when compared with those of neat PBZ matrix. Furthermore, 5 wt% FGO-reinforced PBZ composite also exhibits an enhanced ultraviolet shielding efficiency (88%), with improved tensile strength (52%) compared with those of neat PBZ matrix. The enhanced properties may be due to homogeneous and uniform distribution of FGO into the PBZ matrix, which was confirmed from scanning electron microscopic and high-resolution transmission electron microscopic images. Data obtained from these studies indicate that the developed nanocomposites with high dielectric constant can be used in the form of coatings, sealants, and encapsulates for high-performance dielectric as well as antistatic applications.

High dielectric permittivity and low loss tangent of polystyrene incorporated with hydrophobic core–shell copper nanowires

Core–shell copper nanowires for improving the dielectric performance of polystyrene.

High dielectric response of 2D-polyaniline nanoflake based epoxy nanocomposites

Nanocomposites of two dimensional nanoflake-like polyaniline fillers reinforced in an epoxy matrix have been synthesised and their dielectric properties have been investigated.

Core-satellite Ag@BaTiO3 nanoassemblies for fabrication of polymer nanocomposites with high discharged energy density, high breakdown strength and low dielectric loss

Dielectric polymer nanocomposites with high dielectric constant have wide applications in high energy density electronic devices. The introduction of high dielectric constant ceramic nanoparticles into a polymer represents an important route to fabricate nanocomposites with high dielectric constant. However, the nanocomposites prepared by this method generally suffer from relatively low breakdown strength and high dielectric loss, which limit the further increase of energy density and energy efficiency of the nanocomposites. In this contribution, by using core-satellite structured ultra-small silver (Ag) decorated barium titanate (BT) nanoassemblies, we successfully fabricated high dielectric constant polymer nanocomposites with enhanced breakdown strength and lower dielectric loss in comparison with conventional polymer-ceramic particulate nanocomposites. The discharged energy density and energy efficiency are derived from the dielectric displacement-electric field loops of the polymer nanocomposites. It is found that, by using the core-satellite structured Ag@BT nanoassemblies as fillers, the polymer nanocomposites can not only have higher discharged energy density but also have high energy efficiency. The mechanism behind the improved electrical properties was attributed to the Coulomb blockade effect and the quantum confinement effect of the introduced ultra-small Ag nanoparticles. This study could serve as an inspiration to enhance the energy storage densities of dielectric polymer nanocomposites.

A comparative study of nano-SiO2 and nano-TiO2 fillers on proton conductivity and dielectric response of a silicotungstic acid-H3PO4-poly(vinyl alcohol) polymer electrolyte

The effects of nano-SiO2 and nano-TiO2 fillers on a thin film silicotungstic acid (SiWA)-H3PO4-poly(vinyl alcohol) (PVA) proton conducting polymer electrolyte were studied and compared with respect to their proton conductivity, environmental stability, and dielectric properties, across a temperature range from 243 to 323 K. Three major effects of these fillers have been identified: (a) barrier effect; (b) intrinsic dielectric constant effect; and (c) water retention effect. Dielectric analyses were used to differentiate these effects on polymer electrolyte-enabled capacitors. Capacitor performance was correlated to electrolyte properties through dielectric constant and dielectric loss spectra. Using a single-ion approach, proton density and proton mobility of each polymer electrolyte were derived as a function of temperature. The results allow us to deconvolute the different contributions to proton conductivity in SiWA-H3PO4-PVA-based electrolytes, especially in terms of the effects of fillers on the dynamic equilibrium of free protons and protonated water in the electrolytes.

Studies on FMCM-41 reinforced cyanate ester nanocomposites for low k applications

The continual development of microelectronics needs insulation materials with lower dielectric constant (low k).

Sustainable high capacitance at high frequencies: metallic aluminum-polypropylene nanocomposites

The high-frequency dielectric response of 0-3 polypropylene nanocomposites prepared with the activated metallocene polymerization catalyst [rac-ethylenebisindenyl]zirconium dichlororide absorbed on the native Al(2)O(3) surfaces of metallic aluminum nanoparticles is characterized. The nanocomposites produced are randomly dispersed in the polyolefin matrix with no visible defects that might degrade film dielectric properties. Electrical measurements show that as the volume fraction of Al nanoparticles is increased, the effective permittivity of the nanocomposites increases, with ε(r) values reaching ~10 at relatively low frequency (1 MHz). Because of the high permittivity and conductivity contrast between the metal nanoparticles and the polypropylene matrix, Maxwell-Wagner-Sillars theory can be applied to model the loss at high frequencies and provide insight into how the nanocomposite high frequency response scales with Al volume fraction. At higher Al nanoparticle volume fractions, mixing theories predict greater densities of nanoparticle aggregates, consistent with the experimentally observed shift of the dielectric relaxation to lower frequencies. Although these nanocomposites undergo the predicted initial dielectric relaxation with increasing frequency, the metallic nanoparticle complex permittivity imbues the higher Al volume fraction materials with relatively high, sustainable permittivities, 6, at frequencies as high as 7 GHz.